This invention relates to a tanker having segregated water ballast tanks sufficient for allowing the tanker to operate safely on ballast voyages without recourse to the use of cargo tanks for water ballast. Therefore, oily ballast water will not be discharged from the tanker.
A known tanker of this type has an inner bottom under cargo tanks, and provides segregated ballast tanks between the inner bottom and hull bottom. This tanker tends toward a bottom heavy condition on ballast voyages owing to the lower position of the water ballast, thus providing worse habitability. In addition, this design requires double bottom tanks of excessively high depth, which results in increasing hull weight and higher building cost.
Another known tanker provides segregated ballast tanks at the same level as the cargo tanks, and, of course, has no inner bottom under cargo tanks. On this type of tanker, damage to the bottom in the event of grounding may readily cause leakage of cargo oil. In addition, single bottom tankers require longer pumping time because cargo oil pump location relative to the cargo tank bottom level is higher than that of the double bottom tanker.